Chandra Astrophysics Institute

Investigation 3: Production of Light - Activity 5

Blackbody Properties

Overview: Students discover that they can determine sizes of stars, if they are modeled accurately by blackbodies.

• Lecture Tutorials on Introductory Astronomy (Adams, et al.): Tutorial on blackbody properties: Students read and complete the hot plate questions and luminosity questions, continuing to Part II about stars and the HR diagram.
• Introduce the HR diagram with the sizes of stars represented. 
• Introduce the relation for a spherical blackbody: L= sigma * T4 * 4pi * R², which relates the luminosity (L in watts = joules/sec), temperature (T, in Kelvin) and radius of the spherical blackbody (R in meters). Sigma= Stefan-Boltzmann constant = 5.67 x 10^-8 Joules / (seconds x meters² x Kelvin⁴) 
  • Image of notes about this relationship: (HR diagram example, LTR relationship)

Teacher tips/tricks:

• Timing: about 1 hour for lecture-tutorial alone

Assessment:

• Compare temperatures and/or sizes of other pairs of objects on HR diagram.
• Ask students to read off properties of selected stars on the HR diagram.